A. Field of the Invention
This invention relates to a magnetic recording medium and a method of manufacturing such a medium, and more specifically relates to a magnetic recording medium in which is formed an uneven pattern, the protruding portions of which comprise magnetic recording elements, and to a method of manufacturing such a medium.
B. Description of the Related Art
Magnetic disk drives are expanding into new application areas and tending toward smaller sizes, and ever-higher recording densities are being demanded of the magnetic recording media mounted in such drives.
A magnetic recording medium comprises magnetic layers and other thin films formed on substrates of aluminum or glass. In response to the above demand there have been unceasing efforts to raise recording densities, by making the magnetic particles comprised by the recording layer finer, modifying materials, reducing magnetic spacing (the distance between the magnetic head and the medium) through improved substrate smoothness, by improvements in the micromachining of magnetic heads, and in various other engineering areas.
However, erroneous writing to areas other than the target track (adjacent tracks) arising from spreading of the recording magnetic field of the magnetic head, as well as crosstalk during reading and other problems have emerged, and limits have appeared to the recording densities achievable through the techniques for improvements used in the past.
On the other hand, a discrete track medium and a patterned medium, in which the recording layer is formed with an uneven pattern in which the protruding portions form recording elements, have been proposed as candidates for magnetic recording media enabling still higher recording densities (see for example Japanese Patent Application Laid-open No. 9-97419). In the case of such magnetic recording media, from the standpoint of magnetic head flying stability, it is thought to be preferable that the depressed portions between the recording elements be filled with a nonmagnetic filling material, and that the upper faces of the recording elements and filling material be made smooth.
Sputtering, CVD, IBD (Ion Beam Deposition), or other dry processes for film deposition may be used as the method of filling the depressed portions with the filling material, for example (see, for example Japanese Patent Application Laid-open No. 2006-85899). Methods may also be used in which a material enabling selection of a fluid state or a hardened state is used, so that, for example, after depositing a film in a fluid state using spin-coating, heating is performed to harden the film (see, for example, Japanese Patent Application Laid-open No. 2005-100496).
Further, in Japanese Patent Application Laid-open No. 2006-92659, by forming a film of a material in a fluid state which enables selection of a fluid state or hardened state as a nonmagnetic member, and filling the depressed portions of the uneven pattern with the nonmagnetic material, depressions and protrusions in the surface of the nonmagnetic material formed following the uneven shape of the recording layer can be reduced.
However, regardless of the method used, it is difficult to selectively fill only depressed portions, and the filling pattern is deposited along the original depressions and protrusions. Hence, if a process is not performed in which filling is stopped at the time at which depressed portions are filled up to substantially the height of the original protruding portions or a greater height, and then the unnecessary filling material on the protruding portions is removed, then a substantially flat surface which can withstand magnetic head flight cannot be obtained.
An ion beam etching method, CMP method, or other machining method can be used as the flattening method (see, for example, Japanese Patent Application Laid-open No. 2006-196143), but in addition to the increase in the number of processes, there are problems with the current technologies.
First, in ion beam etching methods, efforts are made to incline the ion beam gun slightly with respect to the main surface which is to be machined, as a means of selectively removing protruding portions. As a result, a huge amount of time is required for etching. In addition, etching of portions other than protruding portions occurs even at a slow etching rate, so that a completely flat surface is not obtained. Moreover, for reasons of the device configuration, simultaneous processing of numerous surfaces is difficult, and so such a method is extremely unsuitable with respect to productivity.
The CMP method can be used to process tens to hundreds of surfaces at once, and is already used in processes to polish substrates for magnetic recording media. However, because thicknesses differ slightly among substrates, if such substrates are polished together, different polished amounts for different substrates result. Hence a process of selecting substrates in advance by thickness becomes necessary. Further, it is not possible to exercise control sufficient to enable polishing of only the protruding portions of numerous surfaces simultaneously with precision on the order of several nanometers, so that once again there are problems with productivity.
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.